On Wednesday 14 December 2016 05:07 PM, Mark Rutland wrote:
On Wed, Dec 14, 2016 at 11:16:17AM +0000, James Morse wrote:
Hi Pratyush,
On 14/12/16 10:12, Pratyush Anand wrote:
On Wednesday 14 December 2016 03:08 PM, Pratyush Anand wrote:
I would go as far as to generate the page tables at 'kexec -l' time,
and only if
Ok..So you mean that I create a new section which will have page table
entries mapping physicalmemory represented by remaining section, and
then purgatory can just enable mmu with page table from that section,
right? Seems doable. can do that.
I see a problem here. If we create page table as a new segment then, how can we
verify in purgatory that sha for page table is correct? We need page table
before sha verification start,and we can not rely the page table created by
first kernel until it's sha is verified. So a chicken-egg problem.
There is more than one of those! What happens if your sha256 calculation code is
corrupted? You have to run it before you know. The same goes for all the
purgatory code.
This is why I think its better to do this in the kernel before we exit to
purgatory, but obviously that doesn't work for kdump.
I see in an earlier message that the need for sha256 was being discussed
in another thread. Do either of you happen to have a pointer to that.
patch 0/2 of this series.
To me, it seems like it doesn't come with much benefit for the kdump
case given that's best-effort anyway, and as above the verification code
could have been be corrupted. In the non-kdump case it's not strictly
necessary and seems like a debugging aid rather than a necessary piece
of functionality -- if that's the case, a 20 second delay isn't the end
of the world...
Even for the non-kdump ie `kexec -l` case we do not have a functionality
to bypass sha verification in kexec-tools. --lite option with the
kexec-tools was discouraged and not accepted. So,it is 20s for both
`kexec -l` and `kexec -p`.
Also other arch like x86_64 takes negligible time in sha verification.
~Pratyush
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